Electronic components include signal transfer units for sending and receiving signals to and from external apparatuses. These signal transfer units for sending and receiving electrical signals to and from external apparatuses need to have high electrical conductivity and are generally made from a base material of copper or copper alloys. Copper and copper alloys are, however, easily corroded by oxygen or corrosive gases in the air. For anti-rust and anti-corrosion purposes, formation of coating layers of multi-layered nickel plating and gold plating films on the base material has been examined.
Patent Document 1 shows, for example, that an electroless nickel film as an underlayer is formed on the base material of a connection terminal and an electroless displacement gold plating film and an electroless reductional gold plating film are formed in this order on the underlayer.
Patent Document 1: Japanese Patent Application Laid-Open No. 2010-37603.